In an optical Wavelength Division Multiplexing (WDM) network, transponders (TxRx) are required to convert signals from the electrical domain to the optical domain (and vice versa) for transmission over optical fiber on a specific WDM wavelength. This function, i.e., electrical to optical and optical to electrical conversion, is required at the nodes where a connection is added and dropped from the WDM network, and at intermediate nodes in the connection where the wavelength must be changed (wavelength conversion) or the signal must be regenerated (to compensate for losses and distortions that occur in the optical transmission over a distance). In a dynamic network, connection requests (i.e., calls) for an optical channel between two nodes arrive and hold the connection for some time and then the connection (call) is torn down. Thus, transponders are only required for a particular dynamic connection for the length of the call. An efficient way to build such dynamic optical networks is to have shared pools of transponders at the nodes where optical connections originate/terminate and at some additional nodes where just wavelength conversion or regeneration is done. When a connection request arrives, as part of the connection setup process, the connection is allocated the transponders it needs from the shared pools, and when the connection is done and disconnected, it returns the allocated transponders to the shared pools. In a dynamic network the shared transponder pools must be provisioned in the switches ahead of time, so when calls for optical connections arrive the needed transponders for a connection are immediately available. The transponder pools are sized to meet a desired call blocking probability (e.g., a typical over-all call blocking probability objective is 10−3 and the blocking probability objective from a lack of needed transponders would be 10−4).
In previous work, small networks (e.g., NSFNET which has 14 nodes) and a small number (<10) of transponders are used in any node. These methodologies do not scale well to large networks (e.g., 100 nodes) with significant traffic loads that would occur in a telecommunications carrier network (e.g., total network load of many terabits per second). In the realistic carrier scale networks, on the order of forty to fifty transponders are required in the larger nodes and two thousand to three thousand transponders are required network-wide. Networks of this scale would overwhelm the algorithmic techniques used in previous research regarding small networks.
In other previous work, network simulations that assume an unlimited number of transponders are available at each node have been performed, and information from those simulations is used to size the transponder pools. The methodology assumes that some number, M, of transponders are available for use and the simulation data is used to determine how to distribute the M transponders. For example, in one approach, the simulations provide a distribution for each node of the number of transponders in use at a random point in time. From those distributions, the average and peak value for each node is determined, and the M transponders are distributed in proportion to either the average or peak values. However, there is no relationship between this method of distributing M transponders and the call blocking probability that would result.
In another approach, unlimited transponders are assumed at each node and some amount of traffic load distribution between node-pairs is also assumed. The load distribution is scaled in incremental steps from low to higher values. At each load step, a “long” simulation is run to determine the maximum number of transponders used at each node (this is called a “high water mark”). This process continues until the sum of the node high water marks equals M, and then that set of high water marks is used for the transponder pool sizes. The load level at this point is called First Load (FL), and it corresponds with the maximum traffic load that can be submitted to the network with M distributed transponders and have blocking performance identical to a network with unlimited transponders in all nodes.
The problem with these previous methods is that they do not explicitly address the desired blocking requirements, and the network could be significantly over provisioned with expensive transponders. Our studies have shown that designs based on simulation “high water marks” are very conservative and significantly over provision the network.
Another problem with previous methods is that they do not consider the sharing of wavelength conversion and regeneration transponders with the transponders used for the add/drop function. It is well known that having a single resource pool serving multiple traffic streams is more efficient than having a separate pool for each individual traffic stream.